The present invention relates to a liquid crystal display device and a liquid crystal panel and more specifically to significant improvements in a viewing angle characteristic of the liquid crystal display device that controls transmission and cutoff of light by applying an electric field to a liquid crystal layer having three-dimensional optical isotropy.
Among liquid crystal display methods to improve contrast and viewing angle characteristic of a twisted nematic (TN) display system, there have been known an in-plane switching (horizontal electric field) display method (hereinafter referred to as an “IPS method”) and a multi-domain vertical alignment display method (hereinafter referred to as a “VA method”). These methods are able to make substantial improvements in viewing angle and contrast over the TN display method.
However, in the IPS and VA methods since the liquid crystal layer is an optically uniaxial medium, if it is used as is, its transmissivity will have a dependency on the viewing angle. Further, the nematic liquid crystal material exhibits light scattering caused by thermal fluctuations of their molecules. In the IPS and VA methods the nematic liquid crystal material enters a black mode when applied with no voltage. So even in the black mode, degradations in contrast due to light leakage caused by scattering are theoretically unavoidable. These problems of optical anisotropy and light scattering are unique to the display devices using the nematic liquid crystal material.
Under these circumstances, a liquid crystal material with an optically three- or two-dimensional isotropy (hereinafter referred to as an “isotropic liquid crystal”) has come to be known in recent years. This isotropic liquid crystal exhibits a characteristics that, when no voltage is applied to the liquid crystal layer, the alignment of the liquid crystal molecules is optically three- or two-dimensionally isotropic and that when a voltage is applied, a birefringence is induced in the voltage application direction. Isotropic liquid crystal materials reported in recent years that have three-dimensional isotropy are smectic blue phase and cholesteric blue phase liquid crystals. Isotropic liquid crystal materials with two-dimensional isotropy are bent type liquid crystal molecules having a so-called bent-core structure. The bent-core structure means a liquid crystal compound aligned vertical to a substrate and exhibits an isotropy in a plane of the liquid crystal layer when no voltage is applied. Other liquid crystal materials known include cubic phase, smectic Q phase, micellar phase and sponge phase liquid crystals.
Harry J. Coles, Nature, Vol. 436, pp. 997-1000 (2005), describes an increased temperature range of the blue phase which has been very narrow in temperature range and difficult to put into practical use with devices. B. R. Acharya, et al., Liquid Crystal Today, Vol. 13. No. 1, pp. 1-4 (2004), describe isotropic liquid crystal materials and their properties in connection with an optical biaxiality of the bent-core structure.
Further JP-A-2006-3840 discloses detailed electrode structures of liquid crystal panels using isotropic liquid crystals.